Multiple chip module (MCM) designs have responded to the need for increasing the number of electronic devices, such as integrated circuits or memory chips, within smaller areas. Initially, MCM technology connected chips or dies in an unpackaged, bare form in an XY plane and not along a Z axis. MCM technology has now allowed the interconnection and stacking of bare chips along the Z axis. Three-dimensional MCM packaging of this type offers higher chip density and less required interconnect density than two-dimensional multiple chip substrates. For an example of one such three-dimensional multi-chip module, see U.S. Pat. No. 5,222,014. While such designs have greatly improved chip density, further refinements in such designs are needed to improve the management of heat and also to further reduce the profile of the multi-chip module, in other words, to further increase chip density while managing and dissipating the heat generated from the multiple chips.
Another disadvantage of two-dimensional MCMs occurs during burn-in. Burn-in is performed to screen out weak chips or dice and validate that each die in a MCM is a known good die (KGD). If a two-dimensional MCM fails during burn-in, the entire module must be discharged or repaired using a costly removal procedure wherein the defective die is removed and replaced with a known good die. Thus, as the number of dice in a two-dimensional MCM increases, the yield for functional modules decreases. By stacking two-dimensional MCMs to create a three-dimensional MCM, each two-dimensional MCM layer can be tested and burned in separately to validate that each two-dimensional MCM layer and dice therein are known good. Thus, the resulting yields for functional three-dimensional modules are greater than two-dimensional modules having equivalent chip or circuit densities. Also, by performing burn-in at the MCM level, known good die testing of each die can be avoided.